1. Field of the Invention
The present invention relates to a melting furnace for a metal such as aluminum.
2. Description of the Related Art
The inventor of the present invention has proposed a metal melting furnace 100 as shown in FIGS. 5 to 7. In FIGS. 5 to 7, a metal melting furnace is comprised of a preheating flue 120 which is provided, on its upper end, with a material inlet opening 121 through which a meltable material is introduced in the preheating flue 120 and, on its lower end, with an inclined hearth 130. The meltable material (metal) introduced in the preheating flue 120 is heated and molten by a melting burner 125 which is oriented toward the lower end of the preheating flue 120. The molten metal is introduced in a molten metal reservoir 135 through the inclined hearth 130.
The temperature of the molten metal M in the reservoir 135 is maintained at a predetermined value by a temperature maintaining burner 136. A meltable material holder 150 having an open lower end is provided in the preheating flue 120, so that there is a gap C between the meltable material holder 150 and the inner furnace wall 122W of the preheating flue 120 that is located on the side opposite to the melting burner 125 (e.g., see Japanese Patent No. 3,225,000 (page 3 and FIGS. 1 to 3)).
In FIGS. 5 to 7, numeral 122 designates the furnace wall which constitutes the preheating flue 120, 123 the operation inspecting hole formed in the furnace wall 122, 124 the door thereof, 126 the separation wall between the preheating flue 120 and the molten metal reservoir 135, 127 the connecting passage formed in the separation wall 126, and 155 the flange provided at the upper end of the meltable material holder 150.
In connection with the molten metal reservoir 135, numeral 137 designates the furnace wall which forms the molten metal reservoir 135, 138 the operation inspecting hole formed in the furnace wall 137, 139 the door thereof, 140 the molten metal discharge portion, 141 the connecting passage formed in a separation wall between the molten metal reservoir 135 and the molten metal discharge portion 140.
In the metal melting furnace 100 constructed as above, as the gap C is provided between the meltable material holder 150 in the preheating flue 120 and the furnace wall surface 122W of the flue 120 on the opposite side to the metal melting burner 125, no meltable material sticks to the furnace wall surface 122W in the meltable material holder 150 and stays in the flue 120. Thus, the problems that the meltable material sticks to the flue and stays in the flue 120 and that were unavoidable in the prior art can be fundamentally eliminated.
Consequently, it is no longer necessary for an operator to perform troublesome routine operations, such as removal of the meltable material which sticks to the inner furnace wall surface 122W of the preheating flue 120 or the hearth 130 and which stays in the flue or on the hearth or cleaning of the flue, etc. Moreover, not only can the durability of the furnace body itself be enhanced, but also the thermal efficiency to the meltable material can be enhanced, thus leading to high productivity.
In the melting furnace 100 mentioned above, however, there is another problem that impurities such as oxide, in the molten metal reservoir 135 must be removed. Namely, impurities such as oxides of various metals contained in the meltable material or non-metallic inclusions are produced during the melting process of the meltable material and are mixed in the molten metal. It is impossible to obtain a clean molten metal without removing the impurities and, accordingly, the quality of a final mold product cannot be enhanced. To this end, in the known metal melting furnace 100, a reactive additive (flux) is introduced in the molten metal in the molten metal reservoir 135 so as to coagulate the impurities and remove them as dross.
However, the removal of the impurities in the molten metal reservoir 135 requires extremely complicated operations to spread the flux on the molten metal surface 135, to stir the molten metal, and to remove the dross using a scraping rod inserted in the operation inspecting hole 138 after the movement of the molten metal has completely ceased. The flux often contains harmful components, such as chlorine or fluorine, which emits smoke (gas) or irritant odor during operation, and thus, the operating environment is strictly restricted.
Usually, the removal of impurities using the flux is conducted at intervals of 8 hours. Nevertheless, due to the complexity of the operations, it is difficult to remove the impurities completely and thus, a part of the impurities reaches the discharge portion 140, and consequently, the quality of the molten metal is deteriorated. Furthermore, the heavy metal oxide settles to the bottom of the molten metal reservoir 135 and forms a deposit which reduces the amount of molten metal which can be stored in the molten metal reservoir 135.
In view of these problems, there is long need in the industry of the filed that the operation to remove the impurities or the like in the metal melting and reserving furnace be simplified. In particular, improved use or reduction of the flux has been highly needed.